The present invention relates to a method of preparing titanium-containing compositions useful in cleaning and activating the surface of ferrous, zinc or aluminum metal and alloys thereof for subsequent reaction with phosphate coating solutions. More particularly, the invention relates to an improved method for preparing solid titanium-containing compositions which does not require the application of any heat to form the dry solid activating compositions.
In the formation of protective phosphate coatings on surfaces of metals, it has been recognized that in many cases, the metal surfaces react slowly with the applied phosphating compositions so that the process may take longer than desired. It also is known that the desirable properties of the phosphate coatings such as corrosion resistance and adhesion of paint films thereto are diminished by incomplete or defective phosphate coatings or by phosphate coatings improperly applied and which are characterized by a coarse, loosely packed crystal structure.
It is desirable, therefore, that the metals be given some type of conditioning pretreatment prior to phosphating to remove contaminants from the surface such as oils, greases and dirts and to activate the metal surfaces so that when the metal surface is immersed in a conventional phosphating solution, there will be produced thereon a fine crystalline coating of phosphate which substantially covers all of the treated surfaces. Solutions which clean and activate the metal surfaces prior to phosphating are desirable and have been described in the prior art.
U.S. Pat. No. 2,743,205 describes an aqueous solution for treating metal surfaces to render them more active on subsequent formation of phosphate coatings thereon which comprises a mixture of a lithium compound and an alkali orthophosphate. The activating compound is prepared by first dissolving a lithium compound and an alkali orthophosphate in water followed by evaporation to dryness.
It also has been suggested that cleaned sheet steel may be pretreated with an activating composition composed of an aqueous solution containing disodiuum orthophosphate and a small amount of an activating metal such as titanium. U.S. Pat. No. 2,516,008 describes activating and cleaning compositions obtained by combining (a) an activating composition composed of disodium orthophosphate and an activating compound of a metal selected from the group consisting of titanium, zirconium, lead and tin, (b) an organic carboxylic acid stabilizer, and (c) an alkaline cleaning composition suitable for cleaning metal surfaces.
U.S. Pat. No. 2,310,239 describes activating compositions comprising disodium phosphate and a titanium compound, and U.S. Pat. No. 2,456,947 describes activating agents which comprise an aqueous solution of disodium phosphate and a water soluble compound of a multivalent metal such as titanium, zirconium, tin and arsenic. British Pat. No. 1,362,031 describes activating compositions for use in metal cleaning liquids which comprises a mixed orthophosphate of titanium and at least one divalent metal selected from the group consisting of barium, strontium and calcium in which the number of equivalents of titanium present does not exceed the number of equivalents of the divalent metal.
U.S. Pat. No. 2,874,081 describes a method for preparing titanium-containing pretreatment solutions having improved activity by controlling the conditions under which the titanium phosphate composition is prepared. The controls include, among other conditions, low temperature initial dispersion of the essential ingredients followed by a subsequent higher temperature aging treatment and drying.